Phosphorus nutrition of European beech under a future warmer and drier climate

Temperate forest productivity may increasingly be limited by shortage of phosphorus (P). First indicators are declining P concentrations and increasing N/P ratios in leaves and fine roots as well as reports on stem growth reductions potentially due to P limitation. Both the predicted increasing temperatures and frequencies and durations of summer droughts in the course of global climate change in combination with continued high atmospheric N depositions are likely to further alter the P nutrition of temperate forest trees in the next decades, either promoting or impairing productivity.
In order to improve predictions of the P nutrition of important temperate forest trees under the conditions of global change, a four-factorial climate chamber experiment with 36 treatments is conducted with European beech (Fagus sylvatica L.) saplings to examine the effects of soil moisture, temperature, N supply, P supply, and their interactions on growth and C allocation, P uptake and use efficiencies, and fine root rhizodeposition.
Treatments are chosen to simulate the expected change in temperature, rainfall, and N deposition in Central Europe: an increase in temperature (18 and 22°C), a decrease in soil moisture (90, 60 and 30 % of field capacity), an increase in N deposition (low and high), and a decrease in P availability (low, moderate, high).
The uptake capacity for P will be measured by labeling with 33P in the Laboratory for Radioisotope Research (LARI) of the University of Göttingen (cooperation with Prof. A. Polle, Forest Botany and Tree Physiology, University of Göttingen). In spring 2015, a selected number of plants will be irrigated with a H333PO4 nutrient solution (activity ca. 1 MBq) to determine P uptake capacity in response to low, moderate and high P availability in the growing medium and to identify efficient P nutrition strategies. In a test run in November 2014 the optimal residence time of the H333PO4 solution was identified (Fig. 1). The radioactivity in the organs will be determined using a WIZARD3 Automatic Gamma Counter and the relative P uptake estimated from the 33P concentration in single plant compartments.
Additionally, the amount of mycorrhization, composition of ECM communities, phloem exudation and microbial P uptake will be analyzed.

Fig. 1: An autoradiogram (phosphorimager; FLA 5100, Fuji) of a beech root system which resided for 20 min to a H333PO4 nutrient solution and was exposed for three days to the imager plates. Fluoresced red colors correspond to components with high 33P activity while those in blue represent those with low 33P activity (?2 Bq).